Why Boston's plants bloom earlier now than 100 years ago

By
Christa Case, Contributor to The Christian Science Monitor /
August 2, 2004

On a 100-acre farm in Middleborough, Mass., Betty Anderson has been taking notes for more than 50 years. "The first thing I do in the morning when I get up - besides getting myself a cup of coffee or tea - is look at the thermometer, and write down the temperature, the weather, and whatever interests me that day."

In countless "Daily Reminder" books, she has noted when the wood ducks return each spring and tracked the growth and flowering of plants in her garden.

But Richard Primack, a biology professor at Boston University (BU), has used Anderson's records as part of a widespread effort to piece together the effects of climate change on the timing of springtime biological events, such as the return of birds and the flowering of plants.

His findings, corroborated by worldwide studies, show that plants and animals are adapting to higher annual temperatures.

Dr. Primack and his research team found that plants at Harvard University's Arnold Arboretum in Boston are flowering eight days earlier on average than they did 100 years ago. This change in flowering time parallels closely the rise in Boston's temperature - 1.5 degrees Celsius - over the same time period.

The results were presented this weekend at the annual meeting of the Society for Conservation Biology in New York.

While similar studies have been done, the arboretum study was unique in its use of herbarium specimens - clipped portions of plants, usually in flower, that are pressed, dried, mounted on paper, and dated. These specimens, in combination with data collected in 2003, enabled Primack's team to determine the trends of flowering times over more than 100 years.This "opens up a whole new way of looking at [the effects of] climate change on biological communities," Primack says, "because there are literally tens of millions of herbarium specimens from all over the world."In a year or two, scientists can use the specimens to track the effects of climate change over the course of a century.

Primack, together with Peter del Tredici, senior research scientist at the arboretum, combed the arboretum's database to find 229 species of flowering plants that were still living and for which they had herbarium specimens in full bloom. The oldest specimen, taken in 1885, was from a tree lilac still flowering today.

In the spring of 2003, Primack's son, Daniel, now a junior at BU, did most of the field work for the project. Using GPS maps provided by the arboretum, he walked the 265 acres once a week, recording the flowering stages of the 229 species.

Abraham Miller-Rushing, a graduate student at BU, analyzed the data from Daniel's observations and the herbarium specimens, as well as the records of Betty Anderson and other amateur naturalists.

"The challenge in using this kind of [amateur] data, from the statistical- analytical point of view, is that the observers aren't always making observations on a regular basis," admits Mr. Miller-Rushing. "But by comparing the trends that we're finding using naturalist observation and using records that were more rigorous, more scientific - [we're seeing that] they correlate quite closely."

Another change Primack and other scientists have noticed in biological communities is that as the climate changes, new species are gaining a stronger foothold, sometimes crowding out native species.

"This is potentially significant for the future of agriculture in the United States," says Primack. "In a way, Boston shows what the rest of the country will look like in 100 years."

Due to the "heat island" effect, by which urban areas' average temperatures rise more quickly than rural areas, Boston has already undergone the 1-degree-Celsius temperature change that is predicted for rural areas in the next century. If average temperatures rise just one degree Celsius, Primack adds, crops such as corn and wheat will no longer grow well in the areas where they are currently grown."

Dr. del Tredici likens these environmental changes to globalization. "A globalized environment is emerging. It's just like the economy - it's happening, and it's not clear we can do anything about it."

But an article he points to in the January 2003 edition of the journal Nature suggests that studies such as Primack's are still worthwhile: "Because anticipation of changes improves the capacity to manage - by acting proactively rather than reactively - it behooves us to increase our understanding about the response of plants and animals to a changing climate."